This application relates to a method for applying a coating fluid. More particularly, the present invention relates to applying coating fluid in a specifically desired longitudinally disposed pattern.
In various product designs, it is desirable to coat one or more stripes of a coating material in a down-web or cross web pattern on a substrate such as a moving paper web or polymeric film web. In some applications, the coating material comprises a pressure sensitive adhesive (either permanent or removable). In particular, such adhesives may constitute pressure sensitive adhesive coatings including microsphere based adhesives, such as those disclosed in U.S. Pat. Nos. 6,296,932, 5,824,748, 5,756,625, 5,714,237, 5,571,617, 5,045,569, 4,495,318, 4,166,152, 3,857,731, and 3,691,140. It is important when processing such microsphere based adhesives that the relatively delicate microspheres themselves not be damaged or ruptured. For example, if the microspheres are cut or sheared, the adhesive materials therein could start to agglomerate, thereby making it difficult to handle the coating material and form a uniform layer thereof on a substrate. Such agglomeration also may cause the adhesive material to adhere to components of the coating equipment or further web processing equipment, thereby necessitating a shut down of the coating process while coating equipment and components are cleaned.
Accordingly, it is quite important that microsphere adhesives be handled delicately in processing and that any shearing of those adhesives in fluid form be done in a manner that would minimize possible shearing of the microspheres themselves. This goal has proved problematic in many processing conditions where metering and further processing of a microsphere adhesive based coating requires such activities as dispensing of the coating through a die under pressure, exposure of the coating to a doctor blade on a roller, or metering under pressure, exposure of the coating to a doctor blade on a roller, or metering of the coating by passing it through a nip between opposed rollers. For instance, if there is insufficient space in a nip between opposed rolls for a microsphere to pass through that nip, it cannot do so. The microspheres are then squeezed out to the sides of the roll and do not accumulate on any coating being deposited after the nip The deficiencies in prior art processes include inadequate transfer of adhesive from an etched gravure application roll to the web, or undue splitting of the coating material in film form during flexographic coating. In addition, the shear sensitivity and/or poor rheological properties of the microsphere adhesive fluid may result in excessive coagulation (i.e., caused by agglomeration of sheared adhesive microspheres) and/or non-uniform coating lay down, which will result in non-uniform streaks of adhesive, mottled adhesive patterns, coating voids or an undesired “orange peel” coating effect which affect the adhesion level of the dried coating.